maths 2u motion - help with questions plz! (1 Viewer)

[flowerp]

Hi every1,
I need help with the following question please:

why is it that the point of inflexion on a displacement time graph represents the time when acceleration is zero????
I'm referring to question 6a) from the 1998 hsc 2u paper

thank you soooo much !!!!!!

 

[StudyOnly]

What do you do when you have to find points of inflections?
You double dash the function and let it equal 0.
Same thing here, if you double dash x-t function you get a-t function and thus the points of inflection on the x-t graph occur when a-t graph is 0.

 

[vernburn]

 

[flowerp]

What do you do when you have to find points of inflections?
You double dash the function and let it equal 0.
Same thing here, if you double dash x-t function you get a-t function and thus the points of inflection on the x-t graph occur when a-t graph is 0.

THANK YOU SOO MUCH !!!

 

[flowerp]

THANK YOU SOO MUCH !!!

 

[flowerp]

Hey, may someone pls help me with this question? i don't understand why the answer is D - why does the particle have decreasing speed if a > 0?
A particle is moving along the x -axis. The displacement of the particle at time t seconds is x metres. At a certain time, velocity = −3 ms−1 and acceleration = 2 ms−2 . Which statement describes the motion of the particle at that time?

(A) The particle is moving to the right with increasing speed.
(B) The particle is moving to the left with increasing speed.
(C) The particle is moving to the right with decreasing speed.
(D) The particle is moving to the left with decreasing speed.

THANK YOU SOOO MUCH FOR YOUR HELP EVERYONE!!!

 

[StudyOnly]

The particle is moving left (because it is negative, conventionally left is negative). It is decreasing speed because it is accelerating to the right direction. i.e. accelerating to the direction opposite to which it is travelling in. This means it is moving to the left with a decreasing speed.

 

[jazz519]

So best to think of this in the physical sense. What does velocity actually mean. It's taking about how fast you are moving in a certain direction

Key words there are moving in a certain direction. The velocity will always be the same direction as which it is moving. So since there is -ve velocity it is moving to the negative direction (which is defined as left)

Now acceleration. Think of this in terms of applying a force. If the acceleration is +ve it means the force is being applied to the right. Which in this case means it is slowing down because you are applying a force to the right and the particle is moving to the left (draw it in a diagram and it will become obvious, you are basically trying to push it back right while it is moving left, so the speed will decrease)

 

[flowerp]

Thank you so much StudyOnly and jazz519 for your response !!!!